In modern wind turbines, the power and rotational speed control takes place by means of changing the rotor blade angle, for the adjustment of which blade adjustment systems are used. Typically, these are hydraulic or electric systems. Furthermore, the adjustment of the blade angle is also used to shut down and interrupt a wind turbine, so the blade adjustment system is the primary braking system of the wind turbine. In order to ensure the availability of the blade adjustment system, power accumulators are used, which, in the event of a failure of the primary power supply of the wind turbine, supply the system with power. In electric blade adjustment systems, accumulators are typically used as the power accumulators, the availability of which is maintained by charging systems. Generally, these power accumulators are self-sufficient for each rotor blade, a charging unit that switches over cyclically to the individual accumulators by means of switching elements typically being used.
An adjusting drive for a rotor blade of a wind turbine is known from DE 10 2005 030 709 A1, which comprises an electric motor and a frequency converter. Connected to the intermediate circuit of the frequency converter is an emergency power supply device, which comprises a power accumulator providing an electric support voltage and having a series connection of accumulator units, for which power accumulator a charging mechanism is provided, which is configured to charge an individual accumulator unit. Furthermore, a switching mechanism is provided, with which an individual one of the accumulator units can be connected to the charging mechanism.
The drawback is that when the charging mechanism fails, the emergency power supply device can no longer be operated, so the wind turbine has to be shut down. Furthermore, no optimal full charge or recharge is possible by means of the cyclic switching over of the charging unit. In particular, the recharging times for each rotor blade add up owing to the use of only one charging unit.
To increase the availability, it is possible to use two charging units and to construct a redundant system by means of a suitable arrangement of the switching elements. The recharging times then still add up, however.
Furthermore, the use of a separate charging unit for each axle is possible. The recharging time is reduced by this but the failure of a charging unit still leads to a failure of the system.